Ptc device, protective circuit module including the same, and secondary battery including the protective circuit module

This application claims the benefit of Korean Application No. 2007-113642, filed Nov. 8, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

1. Field of the Invention

Aspects of the present invention relate to a secondary battery, and more particularly, to a Positive Temperature Coefficient (PTC) device, a Protective Circuit Module (PCM) including the PTC device, and a secondary battery including the Protective Circuit Module (PCM).

2. Description of the Related Art

Among the types of prismatic secondary batteries, a bare cell generally comprises a can, electrode assemblies stored in the can, and a cap assembly connected to the can. Safety devices such as Positive Temperature Coefficient (PTC) devices and thermal fuses are installed outside bare cells. Each safety device is connected to at least one electrode terminal of a bare cell and the device blocks current from flowing outside the bare cell when the battery temperature rises, or the battery voltage falls below or rises above a reference voltage because of excessive charge and discharge. PTC devices prevent batteries from damage and deterioration.

PTC devices have recently been installed in Protective Circuit Modules (PCM\'s). Solder-based surface mount technologies can be used in order to mount the PTC device. For example, in a Protective Circuit Module (PCM) in which an electrical terminal having a conductive layer is exposed, the terminal of a PTC device is disposed on the electrical terminal having a conductive layer. The Protective Circuit Module (PCM) passes through a high temperature region. The conductive layer on the surface of the electrical terminal of the Protective Circuit Module (PCM) melts and then hardens so that the terminal of the PTC device is both electrically connected to the electrical terminal of the Protective Circuit Module (PCM) and is physically fixed thereto.

However, PTC devices are generally long with respect to the dimensions of a bare cell or PCM and both ends thereof in the length direction are formed as terminals in order to connect a PTC device to bare cells or Protective Circuit Modules (PCM\'s). Since only one terminal is disposed on the conductive layer of the electrical terminal of any one Protective Circuit Module (PCM), the original directions in which PTC devices are disposed may twist out of the designed orientation because of external forces during the manufacturing process or when the conductive layer melts in the high temperature region. This causes a problem in welding bare cells and the terminal as well as causes an external short-circuit since a portion of the PTC devices goes beyond the range of thickness of the bare cells.

Conventional PTC devices are connected to Protective Circuit Modules (PCM\'s) by soldering on surface mount devices (SMDs) using a surface mount technology (SMT). Although the SMT is used to mount PTC devices on SMDs by soldering, since one side of the PTC devices is fixed by a solder method but the other side thereof is not fixed by the solder method, PTC devices may sway or twist either during a mounting process or a subsequent process.

Aspects of the present invention provide a Positive Temperature Coefficient (PTC) device that does not sway or twist when it is being mounted on a Protective Circuit Module (PCM) or subsequently, the Protective Circuit Module (PCM) including the PTC device, and a secondary battery including the Protective Circuit Module (PCM).

Another aspect of the present invention provides a Positive Temperature Coefficient (PTC) device comprising: a PTC main body; a conductive layer contacting the upper surface of the PTC main body; a conductive plate contacting the lower surface of the PTC main body; and a support portion formed in the conductive plate, wherein the support portion has the same height as the upper side of the conductive layer substantially corresponding to the height between the conductive plate and an edge thereof upward.

The support portion is formed by bending one end of the conductive plate. The conductive plate comprises a lower end plate in which the PTC main body is placed, a higher end plate in which the support portion is formed, and a connecting portion for connecting the lower end plate and the higher end plate in a stepped manner. The conductive layer is a plate formed of nickel or nickel alloy.

Another aspect of the present invention provides a Protective Circuit Module (PCM) for a secondary battery comprising: a circuit board main body; a conductive pattern installed in the circuit board main body; and a PTC device comprising a PTC main body, a conductive layer contacting the upper surface of the PTC main body and electrically connecting to the conductive pattern, a conductive plate contacting the lower surface of the PTC main body, and a support portion formed as part of the conductive plate, wherein the support portion has the same height as the height of the conductive layer substantially corresponding to the height between the conductive plate and an edge thereof upward.

The conductive plate comprises a lower end plate in which the PTC main body is placed, a higher end plate in which the support portion is formed, and a connecting portion for connecting the lower end plate and the higher end plate in a stepped manner. An adhesive is coated on the lower surface of the circuit board main body that contacts the support portion. The adhesive may be a thermoplastic or thermosetting adhesive. A welding hole is formed in an area of the circuit board main body that overlaps the higher end plate.

The conductive layer of the PTC device in one aspect of the present invention constitutes a part of the PTC device and may be formed on the surface of the electrical terminal. Thereafter, the conductive layer is placed between the PTC main body and one electrical terminal of the whole Protective Circuit Module (PCM), and all become one integral piece.

Another aspect of the present invention provides a secondary battery comprising: i) a bare cell; ii) a Protective Circuit Module (PCM) electrically connected to the bare cell, wherein the Protective Circuit Module (PCM) comprises: a circuit board main body and a conductive pattern installed in the circuit board main body; and iii) a PTC device comprising a PTC main body, a conductive layer contacting the upper surface of the PTC main body and electrically connected to the conductive pattern, a conductive plate contacting the lower surface of the PTC main body, and a support portion formed in the conductive plate, wherein the support portion has the same height as the height of the conductive layer substantially corresponding to the height between the conductive plate and an edge thereof upward, and wherein one terminal of the bare cell is electrically connected to the conductive plate.

The one terminal of the bare cell is an electrode terminal, wherein a welding hole is formed in an area of the circuit board main body that overlaps the electrode terminal, and the electrode terminal and the conductive plate are combined in an area of the circuit board main body that overlaps the welding hole.

The conductive plate comprises a lower end plate in which the PTC main body is placed, a higher end plate in which the support portion is formed, and a connecting portion for connecting the lower end plate and the higher end plate in a stepped manner. The electrode terminal protrudes from the surface of the cap plate, the lower surface of the higher end plate and the upper end of the electrode terminal contact each other, and the step between the lower surface of the higher end plate and the lower surface of the lower end plate is smaller than the height of the electrode terminal that protrudes from the cap plate. An adhesive is coated on the lower surface of an insulating board that contacts the support portion.

Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.